Twin spool gas turbine engines and other kinds of rotating machinery may include concentric shafts which rotate at different speeds or in opposite directions. In some cases one shaft may be supported from the other through a bearing. It is typical of the prior art to bring oil to the inner race of a bearing through passageways in the shaft to which the inner race is attached. If the bearing is external of the outer shaft, and if the oil supply for the bearing comes from within the inner shaft, the oil must be brought across the annulus between the inner and outer shaft and thence to the inner race of the bearing. Depending upon the bearing and shaft arrangement and the relative axial velocity of one shaft to the other, certain problems may arise in transferring the oil from the inner shaft radially across the annulus to the outer shaft. For example, due to large centrifugal forces, it is difficult to prevent the oil from splashing as it strikes the outer shaft after flowing across the annulus. Splashing produces an oil mist within the annulus which can be swept away by air flow through the annulus. Over a period of time the loss of oil may be significant. If temperatures, temperature gradients and the relative angular velocities of the shafts permit, annular intershaft seals may be disposed on either side of the oil stream flowing across the annulus to prevent loss of the oil mist. Close seals may not be possible in situations where high temperatures, large thermal gradients, and high relative angular velocities are present. It is to these latter problems that the present invention is directed.
Commonly owned U.S. Pat. No. 3,756,672 is directed to damping shaft vibrations of two concentric rotating shafts wherein one shaft is supported from the other shaft by means of a bearing disposed therebetween. Several bearing and shaft arrangements are shown. None of them appear to have the problems which the present invention is intended to solve.